1. Field of Invention
The present invention relates to an apparatus for growing a single crystalline ingot like a round-pillar type that enables the growth of liquid state silicon into the single crystalline state.
2. Discussion of Related Art
A silicon wafer for the fabrication of various electronic devices such as semiconductors and the like is provided by thinly slicing a single crystalline silicon ingot. A single crystalline silicon ingot is fabricated by melting polycrystalline silicon into a liquid state and then by growing a crystal by the Czochralski method (hereinafter abbreviated as the Cz method) or the like.
As the defect characteristics inside an ingot depend on the sensitivity of the growing and cooling conditions of a crystal, efforts have been made to control the species and distributions of crystal growing defects by controlling the thermal environment near a crystal growing interface.
As the melted-down silicon is solid-crystallized, point defects of a vacancy type and an interstitial type are engaged over equilibrium concentration so as to develop into grown crystal defects. The Voronkov theory introduced in xe2x80x9cThe Mechanism of Swirl Defects Formation in Siliconxe2x80x9d (Journal of Crystal Growth 59 (1982), pp. 625) by V. V. Voronkov teaches that such defect formation is closely related to a V/G ratio, where V is a pulling rate of an ingot and G is an axial temperature gradient near the crystal growing interface.
Based on the Voronkov theory, a vacancy type defect occurs when the VIG ratio exceeds a critical value, while an interstitial type defect occurs when the V/G ratio is lower than the critical value. Therefore, the pulling rate has an influence on the species, sizes, and density of the defects existing in the crystal when a crystal is grown according to a given growing environment of a predetermined hot zone.
Generally, the axial temperature gradient G increases radially from the center of the ingot to the edge. Thus, the vacancy type crystal defect region tends to occur at the center of the ingot, while the interstitial type crystal defect occurs most frequently at the circumference. Such defects are observed as COP (crystal originated particle), LDP (large dislocation pit), OSF (oxidation-induced stacking fault) or the like, at a surface of the wafer after predetermined treatments thereon such as etching, heat-treatment, and the like.
Accordingly, in order to restrict the generation of the vacancy type crystal defects at the center thereof when growing the crystal, as well as the interstitial type crystal defects at the circumference, an axial temperature gradient deviation xcex94G, i.e., the difference between the axial temperature gradient Gc of the central part of the single crystalline ingot and the axial temperature gradient Ge of the circumferential part of the single crystalline ingot, in the radial direction of the crystal on the single crystalline ingot, should be reduced and an average axial temperature at the growth interface improved.
In order to reduce the axial temperature gradient deviation xcex94G in the radial direction of the crystal in the single crystalline ingot, the axial temperature gradient Gc should be increased or the axial temperature gradient Ge at the circumferential part should be decreased.
However, the average axial temperature gradient of the growth interface of the single crystalline ingot is reduced when the axial temperature gradient deviation xcex94G is decreased by reducing the axial temperature gradient Ge of the circumferential part, thereby reducing the growth rate of the single crystalline ingot.
Accordingly, efforts have been made to develop an apparatus for growing a single crystalline ingot that will reduce the generation of crystal defects and improve the growth rate, more particularly, to a thermal shield having a direct effect on the thermal environment at the growth interface.
FIG. 1 shows a schematic cross-sectional view of an apparatus for growing a single crystalline ingot according to a related art. Referring to FIG. 1, a quartz crucible 13 containing a meltdown silicon 15 is installed in a chamber of an apparatus for growing a single crystalline ingot. The quartz crucible 13 is coated with a crucible support 17, the surface of which is made of graphite. The crucible support 17 is fixed on a rotational axis 19, which is rotated by a driving means (not shown in the drawing), thereby rotating the quartz crucible 13 to be driven upward.
The support 17 wrapping the quartz crucible 13 is surrounded at a predetermined interval by a cylindrical heater 21 which is surrounded by a thermos 23. In this case, the meltdown silicon 15 is provided by melting a polysilicon lump of high purity in the quartz crucible 13 using the heater 21.
At the upper part of the chamber 11, a pulling means (not shown in the drawing) for pulling an object by winding a cable 33 is installed, wherein the pulling means is rotational. At a lower part of the cable 33, a seed crystal 31 for growing a single crystalline ingot 29 by being pulled up while being contacted with the meltdown silicon 15 is set therein.
At the upper part of the chamber 11, a supply pipe 25 is established for supplying the growing single crystalline ingot 29 and the meltdown silicon 15 inside the crucible 13 with inert gas from the outside. At the lower part of the chamber 11, an exhaust pipe 27 exhausting the used inert gas outside is established.
A thermal shield 35 consisting of first, second and third shielding parts 37, 39 and 41 and surrounding the single crystalline ingot 29 is installed between the growing single crystalline ingot 29 and the crucible 13. In this case, the first shielding part 37 has a cylindrical shape which cuts off radiant heat from the heater 21, the second shielding part 39 has a flange figure connected to an upper part of the first shielding part 37 and is fixed to the thermos 23, and the third shielding part 41 is connected to a lower part of the first shielding part 37 and has a triangular cross-section that protrudes toward the single crystalline ingot 29.
In addition, a bottom of the third shielding part 41 is separated from the meltdown silicon horizontally by a predetermined interval to prevent the radiant heat generated from the meltdown silicon 15 from being transferred to the upper part of the chamber 11 so as to accumulate the heat near the growth interface of the single crystalline ingot 29. Thus, the temperature difference between the circumferential and central parts of the ingot is reduced near the growth interface, thereby reducing the axial temperature gradient deviation xcex94G. Therefore, the generation of defects due to the temperature difference between the central and circumferential parts of the single crystalline ingot 29 growing at a predetermined pulling rate is reduced. In addition, an interior of the third shielding part 41 is filled with a material having an excellent insulating property and becomes an adiabatic part 43 preventing heat from being transferred to the upper part of the ingot 29.
Unfortunately, the apparatus for growing a single crystalline ingot according to the related art only accumulates the heat near the growth interface between the third shielding part and the meltdown silicon by preventing the radiant heat radiated from the meltdown silicon from being transferred to the upper part of the chamber by the third shielding part of the thermal shield.
Therefore, a number of crystal defects are generated due to the large axial temperature gradient deviation xcex94G in the radial direction of the crystal since the temperature hardly rises on account of the concentration failure of the accumulated heat at the circumferential part of the single crystalline ingot.
Moreover, the average axial temperature gradient is reduced at the growth interface as the heat radiation of the central part is inhibited by the heat accumulated at the upper part between the third shielding part and the meltdown silicon, thereby reducing the growth rate thereof.
Accordingly, the present invention is directed to an apparatus for growing a single crystalline ingot that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide an apparatus for growing a single crystalline ingot that reduces the generation of growth defects by decreasing the difference between the axial temperature gradients of the central and circumferential parts of a growing single crystalline ingot.
Another object of the present invention is to provide an apparatus for growing a single crystalline ingot that enables improvement of the growing rate of a single crystalline ingot by increasing an average axial temperature gradient at the growth interface of a single crystalline ingot.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention comprises a chamber; a quartz crucible established in the chamber for growing a single crystalline ingot with a predetermined diameter D which is to be put in the quartz crucible; a crucible supporter wrapping the quartz crucible and fixed to a rotational axis; a cylindrical heater surrounding the crucible supporter; a thermos surrounding the cylindrical heater, the thermos preventing heat radiated from the heater from propagating into a wall of the chamber; and a thermal shield.
The thermal shield includes a first cylindrical shielding part installed between the single crystalline ingot and the crucible; a second flange type shielding part connected to an upper part of the first shielding part, the second shielding part fixed to the thermos; and a third shielding part connected to a lower part of the first shielding part, the third shielding part protruding in the direction of the single crystalline ingot.
The third shielding part further includes a first face having a first horizontal corresponding distance W1 and a first radius of curvature R1, the first face confronting the single crystalline ingot and the meltdown silicon; a second face having a second horizontal corresponding distance W2 and a second radius of curvature R2, the second face confronting the heater and the meltdown silicon in an opposite direction from the single crystalline ingot; a third face confronting a circumferential face of the single crystalline ingot; and a fourth face having a third radius of curvature R3, the fourth face confronting an upper part of the chamber.
In another aspect, the present invention comprises a chamber; a quartz crucible established in the chamber for growing a single crystalline ingot with a predetermined diameter D which is to be put in the quartz crucible; a crucible supporter wrapping the quartz crucible and fixed to a rotational axis; a cylindrical heater surrounding the crucible supporter; a thermos surrounding the cylindrical heater, the thermos preventing heat radiated from the heater from propagating into a wall of the chamber; and a thermal shield.
The thermal shield includes a first cylindrical shielding part installed between the single crystalline ingot and the crucible; a second flange type shielding part connected to an upper part of the first shielding part, the second shielding part fixed to the thermos; and a third shielding part connected to a lower part of the first shielding part, the third shielding part protruding in the direction of the single crystalline ingot.
The third shielding part further includes a first face having a first horizontal corresponding distance W1 and a first convex radius of curvature R1, the first face confronting the single crystalline ingot and the meltdown silicon; a second face having a second horizontal corresponding distance W2 and a second convex radius of curvature R2, the second face confronting the heater and the meltdown silicon to an opposite direction from the single crystalline ingot; a third face confronting a circumferential face of the single crystalline ingot; and a fourth face having a third concave radius of curvature R3, the fourth face confronting an upper part of the chamber.
In a further aspect, the present invention comprises a chamber; a quartz crucible established in the chamber for growing a single crystalline ingot with a predetermined diameter D which is to be put in the quartz crucible; a crucible supporter wrapping the quartz crucible and fixed to a rotational axis; a cylindrical heater surrounding the crucible supporter; a thermos surrounding the cylindrical heater, the thermos preventing heat radiated from the heater from propagating into a wall of the chamber; and a thermal shield.
The thermal shield includes a first cylindrical shielding part installed between the single crystalline ingot and the crucible; a second flange type shielding part connected to an upper part of the first shielding part, the second shielding part fixed to the thermos; and a third shielding part connected to a lower part of the first shielding part, the third shielding part protruding in the direction of the single crystalline ingot.
The third shielding part further includes a first face having a first horizontal corresponding distance W1 and a first concave radius of curvature R1, the first face confronting the single crystalline ingot and the meltdown silicon; a second face having a second horizontal corresponding distance W2 and a second convex radius of curvature R2, the second face confronting the heater and the meltdown silicon in an opposite direction from the single crystalline ingot; a third face confronting a circumferential face of the single crystalline ingot; and a fourth face having a third concave radius of curvature R3, the fourth face confronting an upper part of the chamber.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.